Beijing has issued an orange alert and has urged residents to stay indoors because of heavy smog which has covered the capital. This is the highest-level smog alert so far this year, and the warning level is second only to ‘red’ in terms of its severity.

The orange alert was issued a day after the level of small particles (so called PM 2.5 particles with a diameter of 2.5 micrometers or less) reached 274 micrograms per cubic meter. The World Health Organization (WHO) considers only 25 micrograms to be a safe level.

The particle level fell below 200 on Sunday but was still considerably higher than that which is deemed safe safe.

Beijing has recommended that residents minimize outdoor activities. People with respiratory diseases as well as the elderly have been urged to stay at home. Under the orange alert, industrial plants must reduce production, construction sites should stop and the usage of large trucks is banned.

According to the municipal weather center, the smog is likely to remain for two more days because of humidity and a lack of wind. On Wednesday, a cold front is going to improve the environmental situation in Beijing.

Environmental issues are very pertinent in China, which produces most of its electricity by burning coal, making it the world’s biggest greenhouse gas emitter.

In March, four types of pollution alerts - blue, yellow, orange and red - were introduced by Beijing's Environmental Protection Bureau. All factories are to be shut down during orange alerts. Heavy vehicles, such as construction trucks, are also completely banned during orange and red alerts.

China, however, is taking measures to battle the ecological issues. On Sunday, Environment Minister Chen Jining reported that China has fulfilled their green program, which is a part of the 12th five-year plan, six months earlier than scheduled.

“Not only are we working to fix our domestic environmental problems, we have made considerable contributions to addressing international challenges, too,” Chen said as cited by Xinhua.

The achievements don’t mean there is no room for improvement, Minister Chen said: 20 million tons of major polluting agents are discharged in China yearly. This number must be reduced by another 30 to 50 percent to see a significant improvement.